Distillation of tar



f ,tw fa C E 4 SheetS-Sheefc 2 fonde/75er A. H. RADSCH DISTILLATION 0FTAR 7rc/'a Original Filed July 8, 1931 INVENTOR @24m AW BY ATTORN EYSFinne 23, 1936. A. H. RADAscH 2,045,407

' DISTILLATION OF TAR original Filed July. 8, 1951 @sheets-'sheet sATTORNEYS .Fume 23,1936. A H, RADASCH 2,045,407

DISTILLATION QF TAR origina-1 Filed Ju1y,. i931 4 sheets-sheet 4INVENTOR @Mam/@4M ATTORNEYS Patented June 23, 1936 DISTILLATION nOF TARArthur H. Radasch, Bloomfield, N. J., assignor to The Barrett Company,New York, N. Y., a corporation of New Jersey Application July 8, 1931,Serial No. 549,419

Renewed January 27,1936

8 Claims.

This invention relates tothe distillation of tar and includes both theprocess and apparatus therefor. More particularly the invention relates2o a novel method of recovering tar acids from It is customary torecover the tar acids from tar by distilling the tar, obtainingA adistillate and extracting the condensed distillate or a fraction of thecondensedv distillate With caustic lsoda, or other alkaline reagent.This necessitates large tanks for the storage of tar-acid oil andextensive equipment for the liquid extraction. The present method doesnot require such storage facilities and does provide a continuousprocess by which .the tar acids are recovered from the vapor phaseconjunction with the tar distillation.

There are many advantages in vapor phase extraction of the tar acids ascompared with extraction in the liquid phase. By vapor phase extractionI refer to bringing the tar-acid vapors in admixture With vapors ofnon-acid or neutral oils into contact with an alkaline reagent wherebysalts of the tar acids are formed and the tar acids are thus recoveredand separated from non-acid constituents Without first condensing them.In order to extract tar acids in the vapor phase without condensing oilsthe extraction must be carried out without any substantial cooling ofthe vapors. In order that the extraction may be effected VWith anaqueous solution it is advantageous'thatV the vapors extracted shall notbe so hot as to evaporate an excessive amount of Water from the solutionbecause such evaporation will cause crystallization or solidilication ofthe solute from the solution and will cool `the vapors and causecondensation. Commercial solutions containing about 47 to 50% of causticcan be used in extracting gases or vapors at temperatures up to 200 C.or somewhat higher, without the evaporation of excessive amounts ofwater.

The temperature of the vapors resulting from distilling the tar may beso high that vapor phase extraction of these vapors is not practicable.Ac-

r ccrding to this invention, therefore, thevapors are cooled in a heavyoil condenser to a temperatureat which they can be extracted with anaqueous solution of an alkaline reagent. Higher boiling oils, includingthe higher boiling tar acids, are condensed in the cooling process Whilethe lower boiling oils including lower boiling tar acids remain in vaporform. Tar acids are distilled from the condensed heavy oil by passing alarge volume of tar-acid-free inert gases through the heavy oil. Thegases and vapors from this inert gas distillation are blended with atleast a partof the vapors of the lower boiling tar acids and neutraloils that are not condensed with the heavy oil. The blended gases arethen extracted VWith an aqueous solution of caustic or other alkalinereagent, which removes tar acids as carbolate and the carbolate soformed includes tar acids that are vaporized from the heavy oilcondensate andalso tar acids that are not condensed with the heavyoiljbut remain as vapors after rcondensing the higherboiling oilsV4 Taracids are thus separated from vapors of non-acid constituents. It isladvantageous to recycle at least a portion of the resulting vaporsthroughrthe heavy oil condensate to aid in the distillation of tar acidsfrom the heavy oil condensate. The tar-acid distillation is thenlselective in so far as vapors of neutral oils in the recycled gases andvapors prevent or inhibit distillation of neutral oils from theheavy-oil condensate. i Y l In this distillationof tar acids from theheavy oil condensate, inert gases such as steamrnay be employed, and atleast in part recirculated'. According to apreferred method, howevergtherecirculated gases include vapors of non-acid constituents present inthe heavy oil or in the noncondensed vapors from the heavy oilcondenser. Gases is used in this application in a broad sense to includenon-condensable gasessuch as nitrogen, etc.,which may be employed in theinert gas distillation, and condensable vapors such'as steam and vaporsof neutral oils.

If desirable, a condenser maybe employed in the cycle before the gasesenter the caustic `tovver and the condenser may be placed in such aposition that it acts upon the recycled gases before or after the vaporsfrom the distillation of the heavy oil are blended with the lowerboiling vapors from the heavy oil condenser; or a condenser may beincluded in the cycle for cooling the vapors after they leave thecaustic extractor. If the condenser precedes the caustic extractor,tar-acid oils are condensed. If the condenser follows the causticextractor, the oils may be neutralpoils or oils of at least relativelylow tar-acid content.

It may be desirable to treat separately the vapors from the heavy oilcondensate with caustic or other'alkaline reagent to recover the taracids present in this heavy oil condensate before blending these vaporsWith the vapors leaving the heavy oil condenser. Further, it may bedesirable'to insert a condenser in this inert gas cycle after such acaustic extractor toV condense separately neutral oils distilled fromthe heavy oil condenai before blending the vvapors'from the'distillation of this heavy oil condensate with the vapors leaving theheavy oil condenser.

Various modiiications of the process are possible within the scope ofthis invention. By condensing and drawing off the heavy oil fractionwithout excessive cooling, condensate is obtained which generallycontains sufcient heat to effect the inert gas distillation of tar acidsTfrom the oil without other heating. Thus the Yentire -heat required forthe distillation of tar acids from the heavy oil condensate may besupplied to the tar in the still. Additional heat may be supplied to thesystem to effect the distillation of tar acids, if necessary ordesirable, as, sfor example,

by heating the oil by heat 'interchange with steam or other heatingmedium before or during the inert gas distillation, or by :heating V.the.'cir'- culated gases, etc. According to the @preferred method, however,the tar acids are vaporized by the self-contained heat of the heavy `oilcondensata l "The vrateatwlflich Ftl'ie inert gases are circulatedthrcughithe hot condensat-e is correlated with'the temperature ofthecondensate so that the desired percentageof the tar 'acidsis-vaporized from the condensate. By limiteddistillation, lowerboilingtar acidscan be obtained, such as a mixture of phenol andtheicresolswhich contains a relatively :small` amount of therv'higher Iboilingacids. By repeated :fractional treatments desired tar-'acid fractionscanbe :obtained vfrom the same condensate.

"The vapors from the tar distillation `may be atsuchihigh'temperaturethat one or more separate .heavy oil fractions maybe condensed beforecondensing a tar-acid oil fraction containing desired taracids.

"The process-is applicable to the treatment of tars, such fas coke-oven-.tars, gas-retort tars, vertical-retort tars and low-temperaturetarsaand other tar-acid vand.neutral-oil-containing hydrocarbonmaterials `such as coal-tar oils. It may be :applied to 4the treatmentof raw, moistureconta-ining taror stripped tar, etc., or Vto theseparate -treatment vof tar :fractions such as the heavy :tar'ffrom thecollector main of a cokeoveniplant, `or the llighttaror tarr-y oilfromthe condensers ofY such `a plant. It may be applied tofthe treatment ofmixtures containing coal tar, etc. The invention will be described moreparticularly -as .applied to :the .treatment of cokeoven tar.

V In :the Ivapor xph-ase extraction of V.tar acids, caustic lsoda hasproven very rsatisfactory, and because-of 'its relative cheapness it isconsidered a :desirable alkaline reagent for use in this connection.@ther neutralizing agents may `be employed.

:It is advantageous -to-lcarry out `thetar distillation-process 'as aYcontinuous .process .in which the Yvapors leave the still lat asubstantially uniform temperature although the invention may alsoibev'applied to a .batch distillation process. When the tarisLcontinuously"distilled apipe still is prefer-red' for 'this purposealthough a .tank still `oripot-still `can be employed. A series ofstills arranged, forexampla on .thecascade principle, may be employed.The heavy-oil-condenser employed may be used fin conjunction with anordinaryJfractionatingcolumn. Selected oil :fractions frornrthercondensing or fractionating .units maybetreated-.fortherecovery.ofgraded .tar acid tractions.

`AThe .tar--acidlstill -in rwhich tar acidsare dis tilled fromthe-heavyoilcondensate .may bea "va-pors from other vapors.

packed tower or a grid tower of the type employed for bringing a gas andliquid into intimate contact, or any other suitable gas and liquidcontact apparatus may be used.

The caustic extractors may likewise be packed towers or grid towers orother apparatus containing suitable spray means. Preferably the causticextractors include more than one Contact chamber in each of which thegases 'are sprayed with caustic for efiiciency in removal of tar acid Inorder to provide -contactwbetween a large surface of the caustic and thevapors it is advisable to recirculate, with the fresh causticY employed,a part of the carbolate alreadyformed. By providing two or more chambersfor the'extraction it is possible to ad- Amitiresh lcaustic to one,recirculate the carbolate 4formed in -it and withdraw carbolate producedin the iinal chamber, as described in connection with thedrawings,without withdrawing any large Apercentage of .uncombined caustic withthis finished carbolate.

fAfter the extraction of tar acids from the vapors from the heavy -oilcondensation, the vapors may be further cooled and oils condensed eitherArractionally .or to .produce a total condensate. These; oils will -berelatively .-free from tar acids, depending upon the thoroughness withwhich tar acids are removed from the vapors during the tar`acid-extraction. They will include -lower boiling the amount of oilremoved vfrom it. If oils are distilled the residuerom the distillationwill be aheavy .oil although in some cases it will be a pitch. Theinvention will be further described in connection with the accompanyingdrawings but .it .isintende'd and is to be lunderstood that itis notlimited thereto. Y

. .-Eig. `1 showsa tar still which includes aheating coil and -vapor boxconnected with a frac- .tionating column especially equipped for therecovery-.of tarV acids;

IFigs. 2 .to 6 are modified forms of the apparatus shown 1in Fig. 1;

Fig. 7 shows apparatus which may be employed inconnection with a simplestill to carry out the invention; and

Fig. 8 shows a series of simple stills arranged for continuousdistillation.

In the drawings the same numeral is employed to indicate like apparatuswith the addition of a distinguishing letter for each different figure.

lAccording to 'the arrangement of Fig. 1, the tar to be .treate'disheated in the coil I of the pipe still and vthen flashed in the vaporbox v2. The vapors are separated from residue which is drawn oil "intothe pitch receiver 3. The vapors pass through the main 4 to the section5 of the fractionating column. Other sections of the fractionatingcolumn are shown at 6 and 1. Between the column sections are coolingcoils V8, 8 and 8".

A heavy oil Vfraction is removed from section 5 by cooling the vapors toa temperature such that the oils condensed contain a. negligible amountof tar acids of commercial value. On further cooling oils will becondensed which will contain desirable 'tar acids. From Vsection 6 anoil is withdrawn which `contains -a :part of the desired tar acids andthe balance of the desired tar acids pass in .vapor form through themain 9 to the caustic extractor .|0. There is no gas or liquid passage-between the Ycooling coils 8 (above sec- 75 bij tion E) and section 1of the column. All of the vapors pass from the cooling section abovesec,- tion 6 through the main 9 to the caustic extractor I0 and vaporspass from the caustic extractor I0 back to section 1 through the mainI0. The vapors enter section at a temperature above that at which theycan be extracted in the vapor phase by caustic. They are cooled by thecooling coils above section 6 to about 200 C. or lower and are passed tothe caustic tower IIJ at this temperature.

The oil withdrawn from the section 6 throug the line 6 enters thetar-acid still I2, which is` shown as a packed tower in which the oil isbrought into intimate contact with inert gases circulated through thelinek I I by the blower II These inert gases cause distillation of taracids from the oil. The tar acids and inert gasespass from the tower` I2through the main I3 and are combined with the vapors leaving the cooler8 of the column and are together treated in the caustic extractor I0. Inthe caustic extractor tar acids are extracted from the vapors andseparated as carbolates. If the extraction of tar acids is thorough, theoil obtained by cooling the vapors following such extraction will be aneutral oil.

Apart of the gases from the caustic tower are recirculated through thetower I2. These gases are relatively free from vapors of tar acids, butcontain neutral oils which repress further distillation of neutral oilsfrom the heavy oil in the tar-acid still I2, but do not interfere withvaporization of tar acids. The residue drawn off from the tower I2 andcollected in the tank I4 will be a neutral oil or oil ofV relatively lowtar-acid content. v v

The caustic 'extractor shown is of a preferred type. Fresh `caustic isintroduced at I5'. The extractor is divided into two sections, each ofwhich preferably contains grids or other means for exposing a largevsurface of liquid to the gases passing through it. In connection witheach section a line I6 is provided for withdrawing carbolate which ispumped by pumpsy I'I through the heat interchangers K IB and sprayedinto the gases through the spray nozzles I9. Finished carbolate is drawnoif through the'line 20 into the receiver 2I. YThe temperatures of thesprayed solutions are preferably so controlled by the heat interchangersI3 that there is substantially no condensation of oils in the causticextractor. If desired, the vapors may be cooled to effect condensationof neutralI oils in the caustic extractor.

As an example of a method of operating theapparatus shown in Fig. 1, itis possible to heat coke'- oven tar of about 3% tar-acid content in thecoil I to a temperature of 400 C. On flashing, the

v vapors leave the vapor box 2 through the main 4 at a temperature ofabout 380 C. and pitch with a melting point of about 210 F. is produced.The vapors are cooled in passing through the section 5 to a temperatureof about 280 C., and the oil drawn oi of the section 5 through theoutlet 5 has a boiling range of about 248 C. to over 400 C. In thesection 6 the vapors are cooled to 200 recirculating the inert gasesthrough this oil at a rate of 150 cubic feet per gallon of oil ltreatedit is possible to reco-ver in the neighborhood of 80 to 90% of thetaracids in the oil.

After extracting the tar acids the vapors are in part` returned to thefractionating column through the line I0', and the balance are recycledthrough the tar-acid still I2 through the line `I I. By the coolingcoils 8 above section 'I of the fractionating column the vapors arefurther cooled and a neutral oil of lower boiling range is obtained. Thevapors are subsequently totally condensed in the final condenser 'I'.Instead of the fractionating column 'I, as shown inFig. 1, the vaporsleaving the caustic extractor may pass directly to the final condenser Iand be totally condensed.`

f In Fig. 2 the vapors pass directly from the vapor box 2a to thecondenser 6a from which the heavy oil condensate is drawn oif to thetar-acid still I2a. The omission of any condenser corresponding to thesection 5 and cooling coils vt of Fig. 1 is possible if the tar isdistilled to lower melting point pitches. It may even be desirable ifhigh melting point pitch is made, collecting the higher boiling oilstogether with intermediate boiling tar-acid-containing oils and drawingboth off together into the tar-acid still. This gives a larger bulk ofoil to be treated in the tar-acid still, but the extra sensible heatcontent of the higher-boiling oils may at times be an aid to the inertgas distillation. 'Ihe condenser 6a may be an indirect condenser inwhichwater or other cooling fluid is circulated through tubes; or part of thecondensate may be cooled and recirculated; or any other suitable type ofcondenser may be used. In Fig. 2 simple condensers are shown forsimplicity, and the caustic extractor is shown for simplicity as asingle packed tower Illa instead of the preferred extractor shown at IE)inFig. 1.

The apparatus of Fig. 3 includes a condenser 22 between the caustictower I 0b andthe taracid still I2b. In the apparatus of Fig. 1 there isno direct gas passage between the sections 6 and 'I of the fractionatingcolumn. All of the gases from the section 5 pass through the main 9 tothe caustic extractor. In Fig. 3 there is an open passage between thesections 6b and 'Ibof the fractionating column. 'I'he main 9h connectswith the caustic tower and the inert gas cycle is maintained underequalized pressure by a portion of the vapors passing from thefractionating column into the caustic extractor IUI) through thisconnecting main. The gases and vapors from the tar-acid still I2?)`combine with these vapors from the iractionating column and the combinedgases and vapors pass to the caustic tower I 0b Where Vthey areextracted to recover tar acids. The resulting vapors pass to thecondenser 22. In this condenser a neutral oil or oil of relatively lowtar-acid content is condensed, depending upon the extentto which taracids are extracted and removed in the extractor ilb. The cooling in thecondenser 22 can be so regulated as to produce an oil of desired boilingrange.

An arrangement similar to Fig. 3 is one in which the condenser is placedbefore the caustic extractor. The vapors from the fractionating columnmay blend with the lgases and vapors from the still |211, either beforeor after passing through the condenser.

In Fig. 4 a condenser 23 is included in the inert gas cycle precedingthe caustic tower |00. Vapors from the tar-acid still I2c are cooled inthe condenser 23 and a portion of the vapors condensed andV recovered astar-acid oil in this condenser before the vapors pass on to the-causticextractor. 'Ihe cooling in the condenser 23 may be so .regulated as toproduce an oil of desired boiling range. A modification of thearrangement shown `in the drawing is one in which the gases and vaporsfrom the still I2C combine with the vapors from the column before theyenterv the condenser 23.

When operating according to Figs. 3 and 4 it is not necessary that thevapors leaving section 6b and section 6c be cooled to 200 C., since thevapors will be combined with the cooler gas of the inert gas cycle. Itis sufficient that the combined gas caustic tower we. cooling in thecondenser 25, an oil of relatively low stream be about 200 C. or lowerbefore being brought into the extractor. The temperature of the vaporsleaving the column through the mains 9b and 9c and the temperature ofthe circulating inert gases are regulated according to the respectiveamounts of each to give the proper operating temperature within thecaustic extractors |01) and Ic.

The oils withdrawn from section 6d of the fractionating column shown inFig. are oils of higher boiling range than those which pass in vaporform to the caustic tower 10d through the main 9d. It may therefore bedesirable to extract tar acids separately from this higher boiling oilbefore blending vapors from the inert gas distillation in the tar-acidstill |2d with vapors from the section 6d. A caustic tower 2S istherefore provided for separately treating these vapors. Caustic issprayed into the tower 24 in order to recover the higher boiling taracids before blending vapors from the still 12d with the vapors from thesection 6d of the fractionating column. By thus separately recoveringhigher boiling tar acids the phenol content of the tar acids recoveredin the caustic tower Id may be increased.

The apparatus of Fig. 6 is somewhat similar to that shown in Fig. 5 butin addition to the caustic tower 2de for extracting higher boiling taracids,

a condenser 25 is shown for fractional condensation of neutral oils inthe inert gas cycle before the vapors distilled in the tower 12e enterthe By careful regulation of the tar acid content is thus separatelycollected. The temperature of the gas leaving the condenser 25 and thetemperature of the gas passing from the column through the main Se areeach regulated so that the temperature of the continuous gases is notabove about 200 C.

A ractionating column with condensers, or simple condensers can beemployed in any of the modifications shown, as desired. In the apparatusof Fig. 3 there is open communication between t-he sections 5b and 1b ofthe fractionating column. In the apparatus of Figs. 1, 2 and 4 to 6 thegases from the sections 6, 6a, etc., when passing to the section 1, 1a,etc., must first pass through the caustic tower I0, Illa, etc.

Fig. '1 shows an arrangement for the continuous distillation of tar andproduction of pitch in a simple, direct-fired still 26. The arrangementis intended for use in connection with a process in which high meltingpoint pitch is produced. The gases pass from the still through thecondensers 5f, Bf, 1f and 28 and the condensation is so controlled thatthe heaviest oil condensed in 5f contains no appreciable amount ofdesired tar acids. The oils from the condensers Bf and 1f aretaracid-containing oils. They are drawn off into the tar-acid still l2f.The vapors from `'the still are cooled in these condensers soV that theyleave the condenser 1j at a temperature in the neighborhood of 200IC.,and the vapors Aleaving this condenser still contain tar acids. Thesevapors combine with the gases and vapors from the tar acid still .I2fand pass through the extractor lf. A portion of the extracted gases and'vapors is recirculated through the tar acid still I2f. Thebalancepasses to thecondenser 28, in which, on further cooling, `an oilfraction substantially free from tar acids is obtained. This oilfraction generally will contain 2% -or less of tar acids depending uponthe extent to which tar acids are removed in the caustic extractor Mib.

' In Fig. 8 a cascade of stills is shown connected with condensers and acaustic extractor for carrying out this invention. The tar enters thestill 30 and after partial distillation ows in Series through thestillsV 3i, 32 and 33 and is progressively distilled as it passesthrough the stills.

The lightest oils are vaporized in the still 30 and higher boiling oilsare progressivelyY distilled from the stills 3|, 32 and 33. The highestboiling oils from the still 33 pass through the `condenser 35 and aresubjected to fractional condensation therein. The residual vaporscombine with the vapors from the still 32 and pass through the condenser36. Similarly, the residual vapors from condenser 36 combine with thevapors from still 3| before passing to the condenser31. The residualvapors from lthe condenser 31 combine with the vapors from the still 30.In an ordinary distillation they pass directly to the worm condenser 34but when tar acids are recovered they are passed through the causticextractor |0g before passing to the condenser 34. g

The cooling in the condenser 35 is'so regulated that the oil fractioncondensed therein contains no considerable amount of tar acids. Thecondensate from the vcondenser 31 and generally also the condensate fromthe condenser 36 contain tar acids. These condensates run into or arepumped by the pump 39 into the tar-acid still l2gin which tar acids aredistilled from the oils by a current of inert gases.' The gases andvapors from the tar acid still |29' are blended with the vapors fromcondenser 31 and from still 30 and are then passed through the causticextractor lg. 'I'he cooling in condenser '31 is so regulated that thecombined vapors entering the caustic extractor Ig are at a temperaturein the neighborhoodof 200 C. or lower and can therefore be extracteddirectly with caustic soda. Part of the extracted vapors arerecirculated and again passed through the tar acid still l2g. Thebalance of the extracted vapors passes through the worm .condenser 34.

Instead of the single condensers arranged in series shown in Figs. `'1and 8, a fractionating column may be employed. In each of thearrangements shown a caustic tower such as that shown in Fig. l is to bepreferred for the extraction of the vapors.

The invention is not limited to the .arrangements shown in .thevdrawings or to the specic processes described. It is defined in theappended claims.

I claim:

l. The method Vof treating tar-acid and neutral-oil-containinghydrocarbon material. which comprises -distilling the material, coolingthe vapors to condense part but not all of the tar acids therebyproducing 'a tar-a'cid-containin-g `condensate, vaporizing tar acidsfrom this condensate, blending-fthe tar acid vapors with uncondensedvapors resulting 'from thesdistillation of 75 the hydrocarbon materialand extracting the blended vapors for tar acids by contact With analkaline reagent.

2. The method of treating tar-acid and neutraloil-containing hydrocarbonmaterial, Which comprises distilling the material, cooling the vapors tocondense part but not all of the tar acids thereby producing atar-acid-containing condensate, vaporizing tar acids from thiscondensate, blending the tar acid vapors with uncondensed vaporsresulting from the distillation of the hydrocarbon material andextracting the blended vapors for tar acids by contact with an alkalinereagent, the vaporization of the tar acids being effected by theself-contained heat of the condensate.

3. The method of treating tar-'acid and neutral-oil-containinghydrocarbon material, which comprises distilling the material, coolingthe vapors to condense part but not all of the tar acid vapors therebyproducing a tar-acid-containing condensate, vaporizing tar acid from thecondensate While still hot in a current of inert gases containingneutral oil vapors, blending the resulting gases and vapors withuncondensed vapors resulting from the distillation of the hydrocarbonmaterial, extracting the blended vapors for tar acids by contact with analkaline reagent and recycling at least a portion of the resulting gasesand vapors to aid in the vaporization of the tar acids from thecondensate.

4. The method of obtaining tar acids from tar, which comprisesdistilling the tar, cooling the distillate vapors to condense part butnot al1 of the tar acids therefrom, thereby producing ataracid-containing condensate, vaporizing tar acids from this condensatewhile still hot, extracting part but not all of the tar acids therefromby contact With an alkaline reagent, blending the resulting tar acidvapors with uncondensed vapors from the distillation of the tar andextracting tar acids therefrom by contact with an alkaline reagent.

5. The method of treating coke oven tar, which comprises heating the tarto a temperature of at least 250 C., flashing the heated tar, coolingthe vapors from the flashing operation to a temperature not above 210C., thereby producing a tar acid oil, vaporizing tar acids from thisoil, blending at leasta portion of the tar acid vapors with uncondensedvapors from the flashing operation, and extracting the combined vaporsby bringing an alkaline reagent into contact therewith.

6. The method of recovering tar acids, which comprises subjecting tar todistillation, cooling resulting vapors to condense a tar acid oil Whileleaving part of the tarI acids in vapor form, vaporizing tar acids fromthe tar acid oil and blending them with the tar-acid-containing vapors,and

then extracting the blended vapors by contact with an alkaline reagent.

'7. The method 0f recovering tar acids, which comprises distilling tarto pitch, cooling the vaporsto a temperature not above 200 C., therebyproducing a tar acid oil while leaving tar acids in the vapor state,vaporizing tar acids from this oil, blending at least a portion of thesevapors with uncondensed vapors from the distilling operation andextracting the combined vapors by contact with an alkaline reagent.

, 8. The method of recovering tar acids, which comprises progressivelydistilling tar in a series of stills, condensing a tar-acid-containingoil from the vapors from one of the stills, vaporizing tar acids fromthis oil, blending these vapors With tar-acid-containing vapors from oneof the other stills and extracting tar acids from the blended vapors bybringing an alkaline reagent into contact therewith. Y

ARTHUR I-I. RADASCI-I.

